Biologic Vertebral Reconstruction

ABSTRACT

A device and method for biologic vertebral reconstruction utilizes a biologically active jacket inserted into a cavity formed in a vertebra to be reconstructed. An artificial bone material is inserted into the biologically active jacket and allowed to set. The structure and method described herein provide for effective biologic vertebral reconstruction. The use of a biological material and artificial bone enables the host bone to replace the artificial bone over a period of time. Additionally, the structure of the biologically active jacket minimizes any impact into the spinal canal and the paravertebral spaces. Moreover, because of its biomechanical characteristics, which approximate the host bone, there is relative protection of the neighboring vertebral against fracture. Still further, the materials of the biologically active jacket may be impregnated with various substances to achieve various advantageous tasks.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/018,507, filed Jan. 23, 2008, pending, the entire content of which ishereby incorporated by reference in this application.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

(NOT APPLICABLE)

BACKGROUND OF THE INVENTION

The invention relates to biologic vertebral reconstruction and, moreparticularly, to devices and methods for biologic vertebralreconstruction utilizing a biologically active jacket inserted into acavity formed in a vertebra to be reconstructed.

Vertebral compression fractures are quite common in the elderlypopulation. These fractures occur following minor injuries orspontaneously in the elderly osteoporotic spine. The other group ofpatients, usually middle aged, is those on long term steroid therapy forconditions such as chronic obstructive pulmonary disease. In the youngerpopulation with normal bone mineralization, vertebral fractures usuallyoccur following high energy injuries such as motor vehicle accidents ora fall from heights.

Until recently, the elderly osteoporotic fractures were treated withpain control and bracing, depending on the severity of pain. However,over the last decade, there has been increasing use of minimallyinvasive procedures such as vertebroplasty and Kyphoplasty, whereby bonecement in a state of low viscosity is injected into the fracturedvertebrae. As the bone cement sets it glues together the fragments ofthe fractured vertebra. Patients usually wake up from anesthesia withminimal discomfort.

As the use of this technique became more common, some adverse effects ofthe treatment have become apparent. At the time of surgery, patients maysuffer from cardio-respiratory failure associated from infusion of largeamounts of polymethylmethacrylate monomers into the circulation; in thecase of vertebroplasty which requires injection of the cement at highpressures, extrusion of the cement into the venous channels andembolization into the pulmonary veins have been described; the cementmay extrude through the cracks in the vertebrae into the spinal canaland compress the spinal cord or the spinal nerves with possible seriouscomplications.

It is now being appreciated by surgeons that reinforcing an osteoporoticvertebra with bone cement may lead to fractures of the adjacent vertebraby compression against a very much hardened neighboring vertebra. Theother concern is the fact that the bone cement will stay permanently inthe vertebra because it is not resorbable. The long term consequence ofthis is not known, hence, its use is generally avoided in youngvertebral fractures.

Treatments of young vertebral fractures are either conservative orsurgical. The conservative approach is usually favored when thedeformity of the vertebra is not severe and when there is no injury toneural elements. However, the biomechanical alterations caused even byan apparently minor deformity may lead to the development of chronicback pain. Surgical stabilization becomes imperative if there is spinalcord injury, usually associated with significant instability of thespine. The stabilization surgery usually involves massive surgicaltrauma through either or both anterior and posterior approaches.

BRIEF SUMMARY OF THE INVENTION

Significant aspects of the described embodiments include: (a) thetechnology involves implantation of a biologic material—artificial boneinto the fractured vertebra such that the host bone will replace theartificial bone over a period of time making this a more suitable optionthan the currently used bone cement; (b) the implant is inserted intothe vertebra in a biologically active jacket, to minimize its extrusioninto the spinal canal and the paravertebral spaces; (c) because of itsbiomechanical characteristics, which approximate the host bone, there isrelative protection of the neighboring vertebrae against fracture; and(d) the walls of the implant jacket may be impregnated with varioussubstances to achieve various advantageous tasks. Examples of theseinclude bone morphogenic proteins to stimulate incorporation of theartificial bone into the host bone, among others.

In an exemplary embodiment, a method of biologic vertebralreconstruction includes the steps of (a) forming a cavity in a vertebrato be reconstructed; (b) inserting a biologically active jacket in thecavity; and (c) injecting an artificial bone material into thebiologically active jacket and allowing the artificial bone material toset. Step (a) may be practiced by drilling. In this context, the methodmay further include a step of collecting bone shavings during thedrilling step. Preferably, step (a) is practiced by drilling in thevertebra to within five millimeters of the vertebra anterior cortex.

Prior to step (b), the method may include impregnating the biologicallyactive jacket with a predetermined substance. The impregnating step mayinclude impregnating the biologically active jacket with a catalyst tospeed up the setting of the artificial bone material injected in step(c). Alternatively, the impregnating step may include impregnating thebiologically active jacket with a bone morphogenic protein to stimulateincorporation of the artificial bone material into the vertebra to bereconstructed. As still another alternative, the impregnating step mayinclude impregnating the biologically active jacket with an antibioticas a prophylaxis against infection.

Prior to step (a), the method may include steps of inserting a trocharand a cannula into a target pedicle of the vertebra to be reconstructed,and removing the trochar, where step (a) is practiced by inserting adrilling tool through the cannula, drilling the cavity, and removing thedrilling tool. In this context, step (b) may be practiced by insertingthe biologically active jacket in the cavity through the cannula.

In another exemplary embodiment, a tool kit for performing biologicvertebral reconstruction, includes a drilling tool including a drill bitfor forming a cavity in a vertebra to be reconstructed, and abiologically active jacket sized for insertion into the cavity. Anartificial bone injector is attachable to the biologically activejacket. Additionally, an artificial bone material is injectable into thebiologically active jacket by the artificial bone injector. The drillingtool may include a biopsy tool attachment for collecting bone shavingsduring drilling for a biopsy specimen. Preferably, the biologicallyactive jacket is formed of various bioabsorbable synthetic materials.

In still another exemplary embodiment, a biologically active jacket foruse in a biologic vertebral reconstruction includes expandable jacketwalls and is sized for insertion into a cavity formed in a vertebra tobe reconstructed. The biologically active jacket is formed of variousbioabsorbable synthetic materials. For example, the biologically activejacket may be formed of polyglycolic acid. Generally, the biologicallyactive jacket may be formed of a synthetic bioabsorbable woven fibernetwork. In one arrangement, the biologically active jacket ismulti-loculated, where loculations include connecting valves made ofoverlapping wall fibers. The jacket walls may be formed as one of singlelayer, double layer, uni-compartmental, multi-compartmental, elastic,inelastic, etc.

The jacket may also be provided with a central fenestrated channel. Inthis context, the central fenestrated channel may be sealed at one endand may include a threaded connection at an opposite end, the threadedconnection being configured to receive a cement injector. The jacket mayadditionally include concentric chambers disposed surrounding thecentral fenestrated channel, where each of the concentric chambers ispartially loculated.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages will be described in detail withreference to the accompanying drawings, in which:

FIGS. 1A and 1B show a longitudinal section view and a transversesection view of a biologically active jacket, respectively;

FIG. 2 illustrates a drill and biopsy tool;

FIG. 3 illustrates an artificial bone injector;

FIG. 4 illustrates the artificial bone injector coupled with thebiologically active jacket; and

FIGS. 5A-5C illustrate the steps in the vertebral reconstruction.

DETAILED DESCRIPTION

With reference to FIGS. 1A and 1B, a preferred embodiment includes ajacket 12 of synthetic bio-absorbable fiber network woven like cloth andmay be uni-compartmental or multi-loculated. If multi-loculated theloculations 14 will have connecting valves 16 made of overlapping wallfibers acting as trap-doors that open up as the chamber is filled withartificial bone to allow filling of the neighboring chambers. The jacket12 has a central fenestrated channel 18 that runs through the length ofthe jacket 12. The channel 18 is sealed at its far end, and the near endis threaded 20 to allow a cement injector to be screwed on.

The multi-loculated design has concentric chambers with the centralchannel 18 running down the center of the innermost chamber. Eachchamber may be partially loculated to reinforce the construct withmultiple networks of fibers to minimize the risk of compression fractureof the implant itself. The artificial bone is injected into the centralchannel 18 from which the cement extrudes into the inner-most chamber.As the chamber 18 fills up, its wall stretches out to open up the valves16 in its outer wall, which then fill up with the artificial bone, fromthe inner chamber, to open the valves in its outer wall, so on and soforth until all the chambers are full. The outer chambers 22 will alsohave fenestrations in the outer wall to allow some artificial bone toextrude and anchor into the host bone. The entire jacket 12 may befitted with a network of channels extending into its interior from theouter wall. These channels will act as a conduit for vascular in-growth.

The fiber network of the jacket 12 may be used as a carrier for variousfactors by impregnating with a material suited for a particular purpose.For example, the material may be bone morphogenic proteins to stimulateosteo-induction and osteosynthesis within the artificial bone,antibiotics as a prophylaxis against infection, or the like.

The artificial bone 24 (FIG. 3), in a preferred embodiment, is in asemi-liquid state which sets into a hard bone within a few minutes afterinjection into the implant jacket 12 in the vertebral body. A catalystmay also be impregnated into the walls of the jacket 12 to speed up thesetting process. The ceramic bone (artificial bone) 24 may be made outof hydroxyapatite or other calcium compounds.

FIG. 2 illustrates a drill and biopsy tool 26 for creating a cavity inthe vertebra to be reconstructed and for taking a biopsy sample. Thedevice 26 includes a drill bit 28 at the tip, and immediately next to itis biopsy tool 30 for shaving of the host bone. The shaving tool 30 ishollow in its center for collection of bone shavings. At the conclusionof the drilling, enough bone shavings will have been collected for abiopsy specimen. The diameter of the shaving tool 30 is the same orslightly larger than the diameter of the unexpanded implant jacket 12.

The artificial bone injector 32 is shown in FIGS. 3 and 4. The injector32 includes a syringe with a plunger 34 that is operated by a screwmechanism 36. As the handle 38 is turned clockwise, the plunger 34 goesdeeper into the syringe and pushes out the artificial bone 24. Thenozzle 40 of the syringe is connected through a screw mechanism to aninjection cannula 42. The injection cannula 42 in turn includes athreaded connector 44 or the like that is engageable with the threads 20on the biologically active jacket 12.

The process of biologic vertebral reconstruction will be described withreference to FIGS. 5A-5C.

The patient is placed on a radiolucent operating table in the prone orlateral position depending on the surgeon's preference. The skin ismarked at the level of the target pedicles with the aid of fluoroscopicvisualization. Through a small skin incision, a trochar and cannula areinserted under fluoroscopic visualization into the target pedicle. Theposition is checked in antero-posterior, lateral and obliqueprojections. The trochar is then inserted deeper into the vertebra toestablish the preferred trajectory. The cannula 42 is then advanceduntil it is at least 3 mm deep to the posterior wall of the vertebra tobe reconstructed. At this point, the trochar is removed leaving thecannula 42 in place.

The drill/biopsy tool 26 is inserted through the cannula, and handdrilling is performed by clockwise turning of the handle. See FIG. 5A.Drilling is carried out to within 5 millimeters of the anterior cortex.The drill/biopsy tool 26 is then removed.

Subsequently, the unexpanded implant jacket 12 is attached to theinjection cannula 42 and is inserted through the cannula 42 to theappropriate depth as determined by fluoroscopically reading the positionof the radio-opaque marker at the advancing tip of the device. See FIG.5B.

The injection cannula 42 is attached to the syringe containing theartificial bone, and the artificial bone is injected while visualizingfluoroscopically. See FIG. 5C.

Exemplary characteristics and properties of the device construction areoutlined below.

1. Implant jacket:

a. Material—polymer of various bioabsorbable synthetic materials such aspolyglycolic acid

b. Wall design

-   -   i. Single layer    -   ii. Double layer wall    -   iii. Uni-compartmental    -   iv. Multi-compartmental    -   v. Elastic    -   vi. In-elastic, folded

c. Implantation mechanism

-   -   i. Create void and then implant    -   ii. Implant to correct deformity as the artificial bone is        injected

d. Filling mechanism

2. Artificial bone

a. Ceramic

b. Host bone

c. Host or ceramic impregnated with radio-opaque material for bettervisualization intra-operatively.

3. Instruments

a. Drill/biopsy tool

b. Artificial bone injection device

4. Technique

a. Prep

b. Insertion of jacket

c. Implantation of the artificial bone

The structure and method described herein provide for effective biologicvertebral reconstruction. The use of a biological material andartificial bone enables the host bone to replace the artificial boneover a period of time. Additionally, the structure of the biologicallyactive jacket minimizes any impact into the spinal canal and theparavertebral spaces. Moreover, because of its biomechanicalcharacteristics, which approximate the host bone, there is relativeprotection of the neighboring vertebra against fracture. Still further,the materials of the biologically active jacket may be impregnated withvarious substances to achieve various advantageous tasks.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A method of biologic vertebral reconstruction comprising: (a) forminga cavity in a vertebra to be reconstructed; (b) inserting a biologicallyactive jacket in the cavity; and (c) injecting an artificial bonematerial into the biologically active jacket and allowing the artificialbone material to set.
 2. A method according to claim 1, wherein step (a)is practiced by drilling.
 3. A method according to claim 2, furthercomprising collecting bone shavings during the drilling step.
 4. Amethod according to claim 2, wherein step (a) is practiced by drillingin the vertebra to within five millimeters of the vertebra anteriorcortex.
 5. A method according to claim 1, further comprising, prior tostep (b), impregnating the biologically active jacket with apredetermined substance.
 6. A method according to claim 5, wherein theimpregnating step comprises impregnating the biologically active jacketwith a catalyst to speed up the setting of the artificial bone materialinjected in step (c).
 7. A method according to claim 5, wherein theimpregnating step comprises impregnating the biologically active jacketwith a bone morphogenic protein to stimulate incorporation of theartificial bone material into the vertebra to be reconstructed.
 8. Amethod according to claim 5, wherein the impregnating step comprisesimpregnating the biologically active jacket with an antibiotic as aprophylaxis against infection.
 9. A method according to claim 1, furthercomprising, prior to step (a), inserting a trochar and a cannula into atarget pedicle of the vertebra to be reconstructed, and removing thetrochar, wherein step (a) is practiced by inserting a drilling toolthrough the cannula, drilling the cavity, and removing the drillingtool.
 10. A method according to claim 9, wherein step (b) is practicedby inserting the biologically active jacket in the cavity through thecannula.
 11. A tool kit for performing biologic vertebralreconstruction, the tool kit comprising: a drilling tool including adrill bit for forming a cavity in a vertebra to be reconstructed; abiologically active jacket sized for insertion into the cavity; anartificial bone injector attachable to the biologically active jacket;and an artificial bone material injectable into the biologically activejacket by the artificial bone injector.
 12. A tool kit according toclaim 11, wherein the drilling tool comprises a biopsy tool attachment,the biopsy tool attachment collecting bone shavings during drilling fora biopsy specimen.
 13. A tool kit according to claim 11, wherein thebiologically active jacket is formed of various bioabsorbable syntheticmaterials.